The problems associated with the transportation of hot feed materials arise from their inherent characteristics, which may include some or all of the following:    (a) The materials are hot (up to 1000° C.), are normally abrasive and normally contain a significant amount of fines. This combination of characteristics has a strong negative impact on mechanical and electrical equipment, to a degree that makes it impractical to use certain equipment and devices which perform satisfactorily over long periods with less aggressive materials.    (b) Once the materials, for example pre-reduced calcined laterite, are exposed to air, they may begin to burn, releasing pollutants which must then be captured.    (c) The process of pre-reduction in a kiln or other device reduces the oxygen content of metallic ores. The subsequent burning in air reverses the reduction process and thereby wastes some of the energy used in reduction.    (d) Certain reduced ores, such as partially reduced iron ore, have a tendency to agglomerate if piled for even short periods of time. Thus, batch transportation in a container with a hopper-shaped bottom may cause sufficient agglomeration in 5-10 minutes to prevent the material from flowing out of the opening in the container bottom.
A typical hot material transfer system might consist of the following:    (a) A valve on the output end of a kiln discharges calcine into a container below, which is mounted on a transfer car.    (b) Once the container is filled, the transfer car travels into the furnace building with the full container, which is then picked up by the furnace-charging crane. The crane raises the container to an elevation just above the top of the furnace feed bins, which are located directly above the furnace.    (c) The crane places the container on the bin and the action of setting the container down causes it to discharge the calcine down into the bin.
The transfer process just described is characterized by significant release of pollutants, at the kiln discharge valve, from the container itself while in transit, and at the loading of the feed bin from the container.
The total distance travelled by the container, vertical and horizontal, is, in a typical case, about 60 meters. The provision of an emission control system, large enough to cover the arrangement just described, and consisting of hood, ducting fan, baghouse and controls, imposes a large financial burden, in both capital and operating costs. Systems using drag chain conveyors or other transportation methods have similar problems.
One transfer system which has been widely discussed but not widely employed, consists of placing the kiln at a higher elevation than the furnace and using gravity to transfer the hot material downwards through closed pipes or ducts. This has the following advantages:    (a) Pollution and dust are eliminated since the material is enclosed at all times and in an oxygen-starved atmosphere.    (b) A continuously discharging source of material can be continuously distributed into the furnace below without resorting to batch feeding the furnace. This is particularly beneficial with an electric smelting furnace.    (e) No complex mechanical/electrical equipment is required which could be adversely impacted by the hot, abrasive, dusty material.
The operational advantages of this system are offset by the very high capital cost involved in locating a kiln or a rotary hearth furnace 30 m± above grade elevation, particularly in areas of high seismic risk.
In practical situations, the material may need to be fed to the furnaces at a substantially different, but usually higher, level than that at which it is discharged from the calcining plant. The calcine needs to be distributed in a controlled manner through multiple feed ports into the furnace.
It is an object of the invention to provide a transfer system which addresses the above problems.